Basal thermal regime affects the biogeochemistry of subglacial systems

Ashley Dubnick,Joel Barker,Brad Danielson,Martin Sharp,Alireza Saidi-Mehrabad

doi:10.5194/bg-17-963-2020

Ashley Dubnick, Joel Barker + Show 3 more

Open Access

https://doi.org/10.5194/bg-17-963-2020

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Abstract

Abstract. Ice formed in the subglacial environment can contain some of the highest concentrations of solutes, nutrients, and microbes found in glacier systems, which can be released to downstream freshwater and marine ecosystems and glacier forefields. Despite the potential ecological importance of basal ice, our understanding of its spatial and temporal biogeochemical variability remains limited. We hypothesize that the basal thermal regime of glaciers is a dominant control on subglacial biogeochemistry because it influences the degree to which glaciers mobilize material from the underlying substrate and controls the nature and extent of biogeochemical activity that occurs at glacier beds. Here, we characterize the solutes, nutrients, and microbes found in the basal regions of a cold-based glacier and three polythermal glaciers and compare them to those found in overlying glacier ice of meteoric origin. Compared to meteoric glacier ice, basal ice from polythermal glaciers was consistently enriched in major ions, dissolved organic matter (including a specific fraction of humic-like fluorescent material), and microbes and was occasionally enriched in dissolved phosphorus and reduced nitrogen (NH4+) and in a second dissolved component of humic-like fluorescent material. In contrast, the biogeochemistry of basal ice from the cold-based glacier was remarkably similar to that of meteoric glacier ice. These findings suggest that a glacier's basal thermal regime can play an important role in determining the mix of solutes, nutrients, and microbes that are acquired from subglacial substrates or produced in situ.

Highlights

Glaciers form by the compression and metamorphism of snow and slowly deform and flow under their own weight
To evaluate how the basal thermal regime affects the biogeochemical materials that glaciers mobilize from the substrate or produce and cycle within subglacial environments, we explore the solutes, nutrients, and microbes found in the basal regions of three fast-flowing polythermal outlet glaciers and the slowflowing western margin of the Devon Ice Cap (DIC, Devon Island, Nunavut, Canada)
We investigated the biogeochemical properties of warm basal ice from three polythermal glaciers that drain a region of the Devon Ice Cap that is underlain by metasedimentary rocks and gneiss

Summary

Introduction

Glaciers form by the compression and metamorphism of snow and slowly deform and flow under their own weight. Subglacial processes, including melt–freeze events and erosion, can result in the production of basal ice near the bed This basal ice is typically characterized by relatively high concentrations of solutes that are dominated by Ca2+, Mg2+, HCO−3 , and SO24− (Tranter, 2006). Basal ice can contain organic matter, nutrients (e.g. phosphorus, silica, potassium), and microbes from the underlying substrate (Montross et al, 2014; Sharp et al, 1999). Both basal ice and subglacial water are known to host populations of microbes that mediate redox reactions Both basal ice and subglacial water are known to host populations of microbes that mediate redox reactions (e.g. Sharp et al, 1999; Wadham et al, 2004), play an active role in bedrock weathering (e.g. Tranter et al, 2002), and produce or consume ecologically important nutrients (e.g. Bottrell and Tranter, 2002; Boyd et al, 2011; Hodson, 2006b; Statham et al, 2008; Tranter et al, 2002; Wadham et al, 2012)

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